The invention relates to the field of optoelectronic components. Optoelectronic components, for example organic-based or hybrid components made of organic and inorganic layers, are widely used in technology.
Organic light-emitting diodes (OLEDs) usually consist of a sandwich structure, wherein there are a plurality of layers of organic semiconducting materials found between two electrodes. In particular, an OLED comprises one or a plurality of emitter layers (EL) in which electromagnetic radiation, preferably in the visible range, is produced by a recombination of electrons with electron holes. The electrons and electron holes are each provided by a cathode or anode, wherein preferably so-called injection layers facilitate the process by lowering the injection barrier. Thus, OLEDs usually have electron injection layers or hole injection layers. Furthermore, OLEDs generally have electron transport layers (ETL) and hole transport layers (HTL) which support the diffusion direction of the electrons and holes to the emitter layer. In OLEDs these layers are formed of organic materials; in hybrid optoelectronic components, the layers can be made partly of organic and partly of inorganic materials.
Compared to conventional inorganic LEDs, OLEDs and hybrid LEDs distinguish themselves by a thin and flexible layer structure. For this reason, OLEDs and hybrid LEDs can have a much more diverse use than traditional inorganic LEDs. Due to their flexibility, OLEDs can be used excellently for screens, electronic paper or interior lighting, for example.
The advantageous properties of optoelectronic components comprising organic semiconducting materials for light generation (OLEDs or hybrid LEDs) can also be transferred to the generation of electricity. Thus, organic solar cells or hybrid solar cells are also distinguished by a thin layer structure, which significantly increases the possible uses compared to conventional inorganic solar cells. The structure of organic solar cells or hybrid solar cells has similarities with OLEDs or hybrid LEDs.
Instead of an emitter layer, however, there are one or a plurality of absorber layers as the photoactive layer. Due to incident electromagnetic radiation, electron-hole pairs are generated as free charge carriers in the absorber layer. The other layers comprise electron transport layers and hole transport layers as well as electron extraction layers and hole extraction layers. These consist of organic materials or in the case of hybrids of organic and inorganic materials, the electrochemical potentials of which are shifted as donor and acceptor layers such that they generate an internal field in the solar cell, which dissipates the free charge carriers to the electrodes. As a result of the incidence of the electromagnetic radiation, electrons are provided on the cathode and electron holes are provided on the anode for generating a voltage or a current.
Due to the thin layer structure, organic solar cells can be produced cheaply and can be applied to buildings over a wide area as film coating.
Further possible applications of optoelectronic components made of organic or inorganic-organic layers are photodetectors, for example. These also use the photoelectric effect, wherein electron-hole pairs are generated in the photoactive layer. Instead of generating electricity, as in solar cells, these are used to detect light, for cameras, for example.
The thin layer structure of the above-mentioned optoelectronic components not only allow significantly more flexible use in everyday life, but is characterised in comparison to the conventional LEDs, solar cells or photodetectors by cost-effective production options.
Conversely, however, a disadvantage of the thin layer structure is a generally lower lifespan of these optoelectronic components compared to conventional structures. In particular, depredation by water vapour or oxygen on the electronic active layers leads to signs of wear and a decreasing efficiency coefficient. Unlike conventional structures, the thin layer structures are not coated by glass or other water or oxygen-resistant materials. The chemical hydrocarbon compounds of organic or hybrid components are also more susceptible to chemical or physical degradation processes.
For this reason, various techniques for encapsulating the optoelectronic components are used in the known prior art in order to prevent permeation of harmful water vapour or oxidation by oxygen.
For example, a method is described in WO 2011/018356, wherein a pressure-sensitive adhesive is applied around an electronic arrangement as a barrier layer. The barrier layer works as a capsule to prevent penetration of permeants and to extend the lifespan of the OLEDs.
In addition, WO 2014/048971 discloses an encapsulation of an optoelectronic component made of an inorganic substance mixture, which is also applied as an adhesive layer. The encapsulation is intended to achieve a hermetic sealing of the electrically active regions of an OLED or a solar cell, in particular against water vapour or oxygen.
In the known prior art, the optoelectronic components are initially produced under a protective atmosphere (usually made of nitrogen). For this purpose, solvent-based processes and thermal vapour deposition in vacuum are used. After the production of the actual organic or hybrid optoelectronic component, this is again encapsulated with a special film or glass to protect it in particular against the effects of oxygen and water. In addition, a thin layer of an absorbent material, a so-called getter material, can usually also be placed between the component and the barrier capsule (e.g. made of glass or a special plastic film). This serves to bind water or oxygen that is already present. As a barrier layer for encapsulation, glass is characterised by a low permeation to water. However, glass is not flexible. For application where a flexible, thin electronic is required, e.g. for displays, sensors, transistors, solar cells, etc. encapsulation is thus usually carried out with a plastic film which has special coatings that form the barrier layer. The plastic film, e.g. PET, PEN or similar, does not usually provide a sufficient barrier effect itself. The barrier property of these films is therefore based on the special coatings and on the following phenomenon: The water or oxygen molecules cannot normally permeate an inorganic blocking layer. However, a perfect thin inorganic blocking layer is never produced, but in the majority of cases small nanometre-sized defects appear, diffuse through the isolated molecules or migrate through them. A second layer, which is diffusion-limiting and placed between the individual inorganic blocking layers, serves to increase the (diffusion) path length of the individual water or oxygen molecules until they again reach a defect in the second blocking layer. The barrier films therefore usually comprise a structure with alternating blocking layers or diffusion barriers and diffusion-limiting layers, which overall lead to an acceptable blocking property and thus prevent permeation of water vapour or oxygen. In the prior art, permeation is usually specified by a vapour transmission rate (VTR) or specifically for water, a water vapour transmission rate (WVTR). Usually WVTR and VTR values for barrier films or barrier substrates from the prior art are between 1 to 10−6 grams water/(24 hours*cm2 barrier surface) or cm3 vapour/(24 hours*cm2barrier surface). The thickness of commercial barrier films or barrier substrates for encapsulation is between 25 to 100 microns (μm). For flexible applications, the barrier film is often applied to both sides of the optoelectronic component in a self-adhesive manner. In the prior art, the individual layers of the barrier film and the entire barrier film themselves do not have an electrical feature for the conduction of the charge carriers, but serve only to protect the component against degradation processes due to water or oxygen.
A disadvantage of the known methods and the use of barrier films is in particular the high layer thickness. Due to a necessary carrier substrate, i.e. Usually a plastic film, as well as the functional barrier layers, i.e. The described inorganic blocking layers (diffusion barriers) as well as diffusion-limiting layers, the overall thickness of a barrier film is at least 50 μm. The optoelectronic component to be encapsulated itself usually only approx. 50 μm thick. With encapsulation on both sides, the encapsulation thus leads to a tripling of the thickness of the component to a total minimum thickness of 150 μm compared to the possible 50 μm. As a result, the component to be encapsulated increases in rigidity and its flexibility decreases. As a result, the possible applications are significantly limited, for example, in relation to electronic paper. In addition, in the encapsulation of the components, problems can occur with barrier films at the edges of the component to be bonded. At these points, due to the flexibility, there is an increased mechanical load and the barrier film may come off despite the adhesive layer and adhesive, which leads to reduced protection and a reduced service life. In addition, during encapsulation, i.e. In particular during the sticking of the barrier films, gas pockets often occur between the barrier film and the component. This increases the failure rate of the produced optoelectronic components and thus the costs. Due to the relatively high costs of the barrier films and the necessity of an additional process step, which increases the likelihood of a defect occurring, the production costs are further increased. In addition, the optical properties may be limited due to reduced transmission and higher dispersion of the barrier films.
Layered OLEDs are also known from the prior art which have individual functional elements, for example electrodes, with barrier-like properties. However, no OLEDs are known with associated individual injection or extraction and transport layers that also have all barrier-like properties to water and oxygen. Furthermore, it is not known to use printing methods for constructing such OLEDs.